In eukaryotes transcription initiation requires the action of several proteins acting in concert to initiate mRNA production. Two cis-acting regions of DNA have been identified that bind transcription initiation proteins. The first binding site located approximately 25-30 bp upstream of the transcription initiation site is termed the TATA box. The second region of DNA required for transcription initiation is the upstream activation site (UAS) or enhancer region. This region of DNA is somewhat distal from the TATA box. During transcription initiation RNA polymerase II is directed to the TATA box by general transcription factors. Transcription activators which have both a DNA binding domain and an activation domain bind to the UAS region and stimulate transcription initiation by physically interacting with the general transcription factors and RNA polymerase. Direct physical interactions have been demonstrated between activators and general transcription factors in vitro, such as between the acidic activation domain of herpes simplex virus VP 16 and TATA-binding protein (TBP), TFIIB, or TFIIH (Triezenberg et al. (1988) Gene Dev. 2:718-729; Stringer et al. (1990) Nature 345:783-786; Lin et al. (1991) Nature 353:569-571; Xiao et al. (1994) Mol. Cell. Biol. 14:7013-7024).
A third factor that is involved in the interaction is the adaptor proteins. It is thought that adaptor proteins serve to mediate the interaction between transcriptional activators and general transcription factors. Functional and physical interactions have also been demonstrated between the activators and various transcription coactivators. These transcription coactivators normally can not bind to DNA directly, however they can "bridge" the interaction between transcription activators and general transcription factors (Pugh and Tjian (1990) Cell 61:1187-1197; Kelleher et al. (1990) Cell 61:1209-1215; Berger et al. (1990) Cell 61:1199-1208).
In humans LEF-1 is a general transcription factor that participates in the regulation of the T-cell receptor alpha (TCR alpha) enhancer. The function of LEF 1 is dependent, in part, on a DNA binding domain that helps to induces a sharp bend in the DNA helix, and on an activation domain that stimulates transcription only in a specific context of other enhancer-binding proteins. The ALY transcriptional activator functions in this context-dependent manner and is a novel LEF 1-interacting protein. ALY is a ubiquitously expressed, nuclear protein that specifically associates with the activation domains of LEF-1 and AML-1, which is another protein component of the TCR alpha enhancer complex. In addition, ALY can increase DNA binding by both LEF-1 and AML proteins.
Overexpression of ALY stimulates the activity of the TCR alpha enhancer complex in cells, whereas down-regulation of ALY by anti-sense oligonucleotides virtually eliminates TCR alpha enhancer activity in T cells. Thus, ALY may mediate specific transcriptional activation by facilitating the functional collaboration of multiple proteins in the TCR alpha enhancer complex (Bruhn et al., (1997) Genes Dev 11(5):640-653).
Accordingly, the availability of nucleic acid sequences encoding all or a portion of ALY transcription coactivator proteins would facilitate studies to better understand transcription in plants and ultimately provide methods to engineer mechanisms to control transcription.